FIThydrowiki - User contributions [en]

Hydropeaking indicator

2020-09-27T20:08:01Z

Dominique Courret:

{{Note|This technology has been enhanced in the FIThydro project! See [[Innovative technologies from FIThydro]] for a complete list.|reminder}}
=Quick summary=
[[file:hydropeaking_indicator_ex1.png|thumb|250px|Figure 1: Example of flow analysis (source: [1]).]]
[[file:hydropeaking_indicator_ex2.png|thumb|250px|Figure 2: Example of flow analysis (source: [2]).]]
[[file:hydropeaking_indicator_levels.png|thumb|250px|Figure 3: Levels of hydrologic perturbation due to hydropeaking events (source: [2]).]]
[[file:hydropeaking_indicator_evolution.png|thumb|250px|Figure 4: Evolution of the Hydropeaking Indicator on the Maronne river at Basteyroux station for the whole year and during the spring (mid-march to mid-june); effect of the progressive implementation of mitigation measures since 2001 (source: [2]).]]
Developed by: French Agency For Biodiversity, Ecohydraulic Team AFB-IMFT, Courret D, Larinier M and Baran P.

Date: 2014

Type: [[:Category:Tools|Tool]]

=Introduction=
Hydropeaking at hydroelectric facilities (more than 150 in France) generates sudden changes in flow in the river and can affect the composition, the abundance and the structure of fish and invertebrates populations over long distances. The objectives of the ''Hydropeaking Indicator'' tool are [1] to characterize peaks within hydrograph and [2] to produce a synthetic indicator of hydrological disturbance, related to the impacts on fish populations.

From the analysis of 97 stations and 1575 years of flow data, rates of change of natural flow variations have been firstly characterized (Figures 1 and 2) in 8 ranges between 5% and 4 times the mean inter-annual discharge. Formulas representing the ''fastest variations possible naturally'' and taking into account the type of change (increase or decrease), the size of the stream (via the mean inter-annual discharge) and the flow range over which the variation takes place have been constructed and then used to discriminate hydropeaks and natural events.

From the analysis of 80 stations and 491 years of flow data affected by hydropeaking, a method was developed to identify, within the hydrograph, hydropeaks whose characteristics are beyond what can occur in natural hydrology, using three criteria: a minimum range (≥ 10% of the mean inter-annual discharge and ≥ 20% of the hydropeak base flow), a minimal rate of change (> to the maximum natural rate of change) and an upper limit on the maximum flow rate (to remove flood events).

A synthetic indicator differentiating five levels of hydrological disturbance induced by hydropeaking regimes was developed (Figure 3). The level of disturbance of each of the 491 years of flow data was evaluated by three expert operators, according to the knowledge of the biological impacts of hydropeaking. The linear discriminant analysis allows reproducing this classification using five characteristic parameters of hydropeaking regimes (87% of correct reclassification).

=Application=
The Hydropeaking Indicator needs discharge time series as input file, with a fixed or variable time step. This time step should be short to precisely describe the hydropeaks (< 0.5-1 h). The indicator can be produced per year or per period corresponding to biological phases / seasons. Its automated calculation requires knowing only the mean inter-annual flow of the river and the maximum turbine discharge of the hydropower plant upstream.

The Hydropeaking Indicator produces [1] a set of parameters that characterizes each hydropeak (base flow, maximum flow, rate of change…) and their statistics, and [2] the score provided by the discriminant analysis and the level of perturbation.

Examples show that the indicator is sensitive to changes in hydropower plant management and allows appreciating the spatial and temporal changes in hydropeaking regimes, including the damping in the downstream direction (Figure 4). This indicator is a tool for managers of "pre-diagnosis" of biological impacts and for monitoring spatial and temporal changes in hydropeaking.

=Relevant mitigation measures and test cases=
{{Suitable measures for Hydropeaking indicator}}

=Other information=
The Hydropeaking Indicator is implemented in an Excel sheet, using a macro coded in Visual Basic. The tool can be transmitted for free by the Ecohydraulics Team AFB-IMFT after agreement.

=Relevant literature=
*[1] Courret D, 2010. Etude des gradients des variations de débit naturelles en vue de la fixation des critères pour le repérage des éclusées hydroélectriques. Rapport GHAAPPE RA.09.04. http://oai.eau-adour-garonne.fr/oai-documents/59478/GED_00000000.pdf
*[2] Courret D, Larinier M, Baran P, 2014. Développement d’une méthodologie de caractérisation des éclusées hydroélectriques et définition d’un indicateur du niveau de la perturbation hydrologique *induite (seconde version). Rapport GHAAPPE RA.14.02.
*[3] Courret D., 2014. Caractérisation de la perturbation hydrologique induite par les régimes d'éclusées hydroélectriques et définition d'un indicateur - Réflexion sur les mesures de mitigation des impacts des éclusées sur les populations de poissons. Thèse de l'INP Toulouse. http://ethesis.inp-toulouse.fr/archive/00002880/

=Contact information=

[[Category:Tools]][[Category:Enhanced in FIThydro]]

Hydropeaking indicator

2020-09-27T20:06:10Z

Dominique Courret:

{{Note|This technology has been enhanced in the FIThydro project! See [[Innovative technologies from FIThydro]] for a complete list.|reminder}}
=Quick summary=
[[file:hydropeaking_indicator_ex1.png|thumb|250px|Figure 1: Example of flow analysis (source: [1]).]]
[[file:hydropeaking_indicator_ex2.png|thumb|250px|Figure 2: Example of flow analysis (source: [1]).]]
[[file:hydropeaking_indicator_levels.png|thumb|250px|Figure 3: Levels of hydrologic perturbation due to hydropeaking events (source: [2]).]]
[[file:hydropeaking_indicator_evolution.png|thumb|250px|Figure 4: Evolution of the Hydropeaking Indicator on the Maronne river at Basteyroux station for the whole year and during the spring (mid-march to mid-june); effect of the progressive implementation of mitigation measures since 2001 (source: [2]).]]
Developed by: French Agency For Biodiversity, Ecohydraulic Team AFB-IMFT, Courret D, Larinier M and Baran P.

Date: 2014

Type: [[:Category:Tools|Tool]]

=Introduction=
Hydropeaking at hydroelectric facilities (more than 150 in France) generates sudden changes in flow in the river and can affect the composition, the abundance and the structure of fish and invertebrates populations over long distances. The objectives of the ''Hydropeaking Indicator'' tool are [1] to characterize peaks within hydrograph and [2] to produce a synthetic indicator of hydrological disturbance, related to the impacts on fish populations.

From the analysis of 97 stations and 1575 years of flow data, rates of change of natural flow variations have been firstly characterized (Figures 1 and 2) in 8 ranges between 5% and 4 times the mean inter-annual discharge. Formulas representing the ''fastest variations possible naturally'' and taking into account the type of change (increase or decrease), the size of the stream (via the mean inter-annual discharge) and the flow range over which the variation takes place have been constructed and then used to discriminate hydropeaks and natural events.

From the analysis of 80 stations and 491 years of flow data affected by hydropeaking, a method was developed to identify, within the hydrograph, hydropeaks whose characteristics are beyond what can occur in natural hydrology, using three criteria: a minimum range (≥ 10% of the mean inter-annual discharge and ≥ 20% of the hydropeak base flow), a minimal rate of change (> to the maximum natural rate of change) and an upper limit on the maximum flow rate (to remove flood events).

A synthetic indicator differentiating five levels of hydrological disturbance induced by hydropeaking regimes was developed (Figure 3). The level of disturbance of each of the 491 years of flow data was evaluated by three expert operators, according to the knowledge of the biological impacts of hydropeaking. The linear discriminant analysis allows reproducing this classification using five characteristic parameters of hydropeaking regimes (87% of correct reclassification).

=Application=
The Hydropeaking Indicator needs discharge time series as input file, with a fixed or variable time step. This time step should be short to precisely describe the hydropeaks (< 0.5-1 h). The indicator can be produced per year or per period corresponding to biological phases / seasons. Its automated calculation requires knowing only the mean inter-annual flow of the river and the maximum turbine discharge of the hydropower plant upstream.

The Hydropeaking Indicator produces [1] a set of parameters that characterizes each hydropeak (base flow, maximum flow, rate of change…) and their statistics, and [2] the score provided by the discriminant analysis and the level of perturbation.

Examples show that the indicator is sensitive to changes in hydropower plant management and allows appreciating the spatial and temporal changes in hydropeaking regimes, including the damping in the downstream direction (Figure 4). This indicator is a tool for managers of "pre-diagnosis" of biological impacts and for monitoring spatial and temporal changes in hydropeaking.

=Relevant mitigation measures and test cases=
{{Suitable measures for Hydropeaking indicator}}

=Other information=
The Hydropeaking Indicator is implemented in an Excel sheet, using a macro coded in Visual Basic. The tool can be transmitted for free by the Ecohydraulics Team AFB-IMFT after agreement.

=Relevant literature=
*[1] Courret D, 2010. Etude des gradients des variations de débit naturelles en vue de la fixation des critères pour le repérage des éclusées hydroélectriques. Rapport GHAAPPE RA.09.04. http://oai.eau-adour-garonne.fr/oai-documents/59478/GED_00000000.pdf
*[2] Courret D, Larinier M, Baran P, 2014. Développement d’une méthodologie de caractérisation des éclusées hydroélectriques et définition d’un indicateur du niveau de la perturbation hydrologique *induite (seconde version). Rapport GHAAPPE RA.14.02.
*[3] Courret D., 2014. Caractérisation de la perturbation hydrologique induite par les régimes d'éclusées hydroélectriques et définition d'un indicateur - Réflexion sur les mesures de mitigation des impacts des éclusées sur les populations de poissons. Thèse de l'INP Toulouse. http://ethesis.inp-toulouse.fr/archive/00002880/

=Contact information=

[[Category:Tools]][[Category:Enhanced in FIThydro]]

Mitigating reduced flood peaks, magnitudes, and frequency

2020-05-05T20:20:20Z

Dominique Courret:

[[file:icon_operation.png|right|150px|link=[[Environmental flow]]]]
[[file:icon_sediment.png|right|150px|link=[[Sediments]]]]

Note that this measure is included in both the environmental flow and sediment categories. In certain FIThydro deliverables the sediment measure is referred to as "Hydraulic conditions for sediment transport".

=Introduction=
[[file:mitigating_flood_orkla.png|thumb|500px|Figure 1: The disappearance of floods in Orkla in mid-Norway due to the river regulation. The blue graph is the observed flow before regulation, while the orange is the flow after regulation. Note that the data series are shown for different time periods.]]

Reservoir-based hydropower will normally lead to a dramatic reduction in floods, unless the flood occurs when the reservoir is more or less filled, or the reservoir is small compared to the inflow. Some reservoirs are built for this purpose, i.e. flood protection. The ecological function of floods to the river system will then also disappear. The reduced frequency of flooding events may result in a deterioration of habitat quality, both by the silting of spawning habitats and the clogging of sheltered habitats. Floods act as 'habitat fresheners' as they remobilise the river bed material, if the floods are sufficiently large and flush out finer sediment fractions. In later sections of this document, habitat measures to refresh the substrate have been described, which will reinstate the natural substrate conditions and improve the habitat. Reinstating floods is one way of refreshing the substrate with use of the flow.
Floods can also have other ecological functions, for instance to facilitate migration and to attract fish for spawning. These floods (freshets) are typically smaller than the natural, annual flood, but the river regulation can also reduce these floods. Such freshets are usually named attraction flow to initiate upstream migration and trigger flow to initiate downstream migration. These floods can also be reinstated, and similar to floods to remobilise the substrate, the magnitude, timing and frequency of these should be when the ecological function is maximised, and the losses in power production minimised.

=[[Methods, tools, and devices]]=

==During planning==
A hydrologic analysis of flood events before and after regulation will also provide data to support the likelihood that reductions in flood frequencies have reduced, or may in the future reduce, long-term production by causing habitat deterioration. To what extent the habitat has been degraded, can be assessed by habitat mapping (Forseth and Harby, 2014).

Some studies make a distinction between armoured and paved layers, related to the resistance of surface layers to floods, e.g. less than 10 years for armour, more than 100 years for pavement. The break-up of the armour layer has been observed for floods with a recurrence interval of at least 7 to 10 years. When the break-up of the armour layer occurs, there is a significant increase in the bedload discharge.

==During implementation==
If properly designed gates and valves are in place, the introduction of a new flow regime would simply be to release the defined water flows at the right time of the day and year. If the existing infrastructure cannot release the proposed flow regime, retrofitting of the dam or any other location the water should be released from, must be carried out.

==During operation==
Hydropower operators must normally document that environmental restrictions are followed, and they would have standard monitoring systems (gauging stations) in place. The improvements in the substrate composition and habitat conditions can be measured by for instance measuring the interstitial space.

Shelter for juvenile salmonids can be measured with a simple method where the number and depth of interstitial species within a given area is counted with use of a rubber tube (Finstad et al. 2009). The number of spaces of varying length are weighed according to their depth and then summed. The number of interstitial spaces within an area of 50 cm * 50 cm, limited by e.g. a steel-frame (Figure 4-5), is counted and the depth registered. The sizes of interstitial spaces are determined based on how far down between the rocks the hose can be inserted.

The effect of the released environmental flow must be surveyed by assessing the development of the fish population, e.g. by monitoring species composition, densities and age structure of populations, number of smolts, etc.

=Relevant MTDs and test cases=
{{Suitable MTDs for Mitigating reduced flood peaks, magnitudes, and frequency}}

=Classification Table=
{{Mitigating reduced flood peaks, magnitudes and frequency}}

=Relevant literature=

Finstad, A.G., Einum, S., Ugedal, O. and Forseth, T. 2009. Spatial distribution of limited resources and local density regulation in juvenile Atlantic salmon. Journal of Animal Ecology 78: 226-235.

Forseth, T. and Harby, A. 2014. Handbook for Environmental design in Regulated salmon Rivers. NINA Special Reports 53. Trondheim: Norwegian Institute for Nature Research.

[[category:Measures]][[Category:Environmental flow measures]][[Category:Sediment measures]]

Mitigating rapid, short-term variations in flow (hydro-peaking operations)

2020-05-05T20:14:05Z

Dominique Courret:

[[file:icon_operation.png|right|150px|link=[[Environmental flow]]]]

=Introduction=
[[file:peaking_params.png|thumb|500px|Figure 1: The figure illustrates the hydropeaking parameters flow ratio (amplitude of change), speed of change and frequency of change in water flow/level.]]
[[file:stranding_ex.png|thumb|250px|Figure 2: Fish using the areas identified by red colour will have a risk of stranding when the water level drops rapidly.]]

Hydropeaking refers to hydropower operations that are characterized by more rapid and frequent changes in power production than typical base-load hydropower production. If the water is released into a river, rapid fluctuations in discharge and water level may cause negative impacts to the riverine ecosystem. The severity of the hydropeaking can be categories according to the magnitude of changes in flow, the frequency of the changes, and the timing of the changes, i.e. what time of the day and year the hydropeaking happens.

Bakken et al. (2016) defines measures to reduce the impacts from hydropeaking operations into three types; i) operational measures that involves adjusting the magnitude, speed of change, frequency and timing of change to the better for the ecosystem exposed to hydropeaking, ii) physical changes in the river system downstream the outlet of the hydropower plant, and iii) technical measures directly on the power plant/infrastructure, i.e. a technical setup that allows a wider range of turbine discharges, slower stop and start-up, etc.

The measures presented in the following are all related to changes in flow.

=[[Methods, tools, and devices]]=
==During planning==
A group of experienced Norwegian scientists summed of a large research project on environmental impacts from hydropeaking operations (CEDREN EnviPEAK - www.cedren.no) by defining a categorisation system for environmentally-adapted hydropeaking operations. The system was developed based on research from EnviPEAK, other similar studies in Norway and across the world, and the expert judgment of the involved scientists. The system was developed primarily based on knowledge about salmonids’ response to hydropeaking. This system is a set of recommendations, seem to have been adopted as standard requirements for hydropeaking operations in Norway, when the environmental terms of operations are revised, or new licences granted. [[COSH-tool]] can be used to find the relevant hydropeaking parameters.

[[file:peaking_params_table.png|600px|Effect factors, indicators and criteria for characterisation (from Bakken et al. 2016 and Harby et al. 2016).]]

The full categorisation system published in Bakken et al. (2016) and Harby et al. (2016) also includes the dimension of assessing the vulnerability of the ecosystem exposed to hydropeaking. The vulnerability is given by assessing factors such as effective population size, degree of limitations in recruitment, habitat degradation, reduced water temperatures and percentage of impacted river length compared to total length. The combined assessment of the effect factors and the vulnerability will give the total and overall impact assessment.

==During implementation==
If the technical system is properly designed with respect to providing environmentally adapted hydropeaking operations, the introduction of a new flow regime would simply be to release the defined water flows at the right speed and time of the day and year. If the existing infrastructure cannot release support slower ramping rates, adjusted water flow and the flexibility of the frequency and timing, a re-building of the infrastructure might be needed.

==During operation==
A new flow regime better adapted to the ecosystem tolerance of hydropeaking operations would normally not introduce any extra maintenance. Hydropower operators must normally document that the environmental restrictions are followed, and would have standard monitoring systems (gauging stations) in place. It should be ensured that the monitoring is made with sufficiently high resolution to capture the rapid changes in water flow due to hydropeaking.

The positive environmental effect of the released environmental flow must be surveyed by assessing the development of the fish population, e.g. by monitoring species composition, densities and age structure of populations, number of smolts, etc.

=Relevant MTDs and test cases=
{{Suitable MTDs for Mitigating rapid, short-term variations in flow (hydro-peaking operations)}}

=Classification table=
{{Mitigating rapid, short-term variations in flow (hydro-peaking operations)}}

=Relevant literature=

Bakken, T.H., Forseth, T. and Harby, A (Eds) 2016. Miljøvirkninger av effecktkjøring: Kunnskapsstatus og råd til forvaltning og industri (in Norwegian).

Harby, A., Forseth, T., Ugedal, O., Bakken, T.H. and Sauterleute, J. 2016. A method to assess impacts from hydropeaking. Proceedings, 11th International Symposium on Ecohydraulics, Melbourne, Australia.

[[category:measures]][[category:Environmental flow measures]]

Mitigating reduced annual flow and low flow measures

2020-05-05T20:10:04Z

Dominique Courret:

[[file:icon_operation.png|right|150px|link=[[Environmental flow]]]]

=Introduction=
[[file:lundesokna_high_low.png|thumb|500px|Figure 1: The photos show Lundesokna in central Norway at different water flows.]]
[[file:Building_block_method.png|thumb|500px|Figure 2: An example of the building block method showing average flow curves before and after regulation, and the key flow blocks. Duration (x-axis, width) multiplied by flow (y-axis, height) provides a measure of the volume of water in question (area of the blocks) and these can be summed to give the reach's "water pool". 1=egg survival and winter habitat, 2=smolt out-migration, 3=flushing flows, 4=juvenile fish growth, 5=juvenile fish habitat, 6=artificial freshets to facilitate angling interests and promote spawning migration, 7=spawning. The colours indicate prioritisation – from orange (high) to blue (low), based on the severity of identified hydrologic bottlenecks.]]
[[file:gauge2.png|250px|thumb|Figure 3: Gauging station monitoring water level and water flow]]
[[file:gauge1.jpg|250px|thumb|Figure 4: Gauging station monitoring water level and water flow]]

Bypass sections of a river regulation will typically experience dramatic reductions in total, annual flow, as large volumes of water are withdrawn for the purpose of producing electricity. The changes will depend on the hydrology characteristics, regulation capacity, the turbine characteristics (i.e. minimum and maximum capacities), the power production pattern and the minimum flow requirements. In cases with limited regulation capacities, spill of water will happen when the inflow is higher than the intake ponds can store and the turbines can utilise. How often this will happen is determined by the hydrological characteristics of the river.

The challenge related to reductions in total, annual flow would be to define ‘how much water is needed to sustain essential habitat qualities’, given dramatic reduced most of the time. This is the most common scientific task related to environmental flow assessments in bypass sections, and downstream the outlet of the hydropower plants in periods the hydropower plant is not in operation. A large set of approaches are available, spanning from simple statistical methods to comprehensive, holistic modelling approaches, with the aim of defining how much water should be released at what period of the year. The more simplified methods would require only a water flow timeseries, while the more advanced would needed detailed measurements of the topography and information about ecological preferences of various flow regimes.

=[[Methods, tools, and devices]]=
==During planning==
The most common method to define environmental flow, or more correctly minimum flow, in Europe is to use of simple statistical criteria (Bakken et al., 2012). Q95 or variants of this is used in several countries as benchmark for the lowest flow releases in rivers with dramatically reduced flows. Q95 refers to the flow that during the natural conditions is exceeded in 95% of the time. Q95 is licence agreement defined as a constant flow that should be released throughout the year, or as a flow level defined based on natural flows during summer and winter, respectively, giving different statistic of flow regime during summer and winter. Bakken et al. (2012) concluded in their review where the practice in a number of European countries were assessed, that the environmental flow requirements are typically in the range 5-10 % of mean annual flow.
In some countries and in selected cases more advanced approaches are used, taking into account the natural variation in flow regime, and the varying flow requirements over the year. The building Block Method (BBM) (Tharme et al., 1998) is one approach, while the environmental design concept (Forseth and Harby 2014) has received very much positivism in Norway from both the hydropower industry, management authorities as well as various stakeholder groups. The Building Block Method intends to define flow regimes that are closer to the natural variation in water flow, i.e. mimicking natural floods, freshets and low flow periods. The environmental design concept aims at identifying the factors limiting the development of the fish population, which can be directly related to the flow regime, and then define the most efficient measures to the lowest cost. The environmental design concept also introduces the ‘water bank’ idea, where the water available for environmental purposes is released during the periods it is most needed.
Hydraulic habitat modelling is a highly sophisticated approach that has been developed since the 1980’s, where the PHABSIM was one of the first computer program for such analysis. Hydraulic habitat modelling has been used in several cases where more detailed studies are required before the water flow regime can be defined, in addition to a large range of purely scientific studies. Hydraulic habitat modelling aims at identifying flows where the habitat conditions are suitable, based on various groups of species’ preferences for hydraulic variable such as water velocity, water depth and substrate conditions. This would sometimes reveal that increasing water flow will not always increase the areas of suitable habitat. Such studies have been carried out mostly related to defining suitable conditions for fish, but is in some cases also applied for benthic invertebrates. Hydraulic habitat modelling would require a 2- or 3-dimensional hydraulic model taking flow as input, and a set of ranges where water velocities, depths and substrate conditions are suitable. Casimir is such a tool that is developed in Germany, but applied in several rivers across Europe, as well as outside Europe. Hydraulic habitat modelling must be considered an ecosystem-based analysis, in contrast to the much simpler statistical approaches, such as applying Q95.

==During implementation==
If properly designed gates and vales are in place, the introduction of a new flow regime would simply be to release the defined water flows at the right time of the day and year. If the existing infrastructure cannot release the proposed flow regime, re-building of the dam or any other location the water should be released from, must be carried out.

==During operation==
Hydropower operators must normally document that the environmental restrictions are followed, and would have standard monitoring systems (gauging stations) in place. The effect of the released environmental flow must be surveyed by assessing the development of the fish population, e.g. by monitoring species composition, densities and age structure of populations, number of smolts, etc.

=Relevant MTDs and test cases=
{{Suitable MTDs for Mitigating reduced annual flow and low flow measures}}

=Classification table=
{{Mitigating reduced annual flow and low flow measures}}

=Relevant literature=

Bakken, T.H., Zinke, P., Melcher, A., Sundt, H., Vehanen, T., Jorde, K. and Acreman, M. 2012. Setting Environmental flows in regulated rivers. SINTEF report Serial No. TR A7246. ISBN 978-82-594-3529-3.

Forseth, T. and Harby, A. 2014. Handbook for Environmental design in Regulated salmon Rivers. NINA Special Reports 53. Trondheim: Norwegian Institute for Nature Research.

Tharme, R., King, J. and De Villiers, M.S. 1998. Environmental Flow Assessments for Rivers: Manual for the Building Block Methodology. Updated adition. WRC Report No TT 354/08.

[[Category:Measures]][[category:Environmental flow measures]]

Environmental flow

2020-05-05T20:07:10Z

Dominique Courret:

=Introduction=
[[File:e-flow.png|thumb|500px|Figure 1: Environmental flow release in Mandal River, Norway]]

Hydropower projects will in most cases change the flow pattern of the affected rivers. The changes in flow are very site-specific and dependent on how the actual project is designed. A hydropower project with a large reservoir for storage of water (‘reservoir-based hydropower’) generally allows much larger changes in flow than a run-of-the river plant. Reservoir-based hydropower can store water from the wet to the dry season and can hence introduce large changes in the periodicity of the flow. Reservoir-based hydropower can also store all or parts of floods, and will typically reduce both the magnitude, peaks and frequency of floods. Run-of-the river plants have limited storage capabilities and will not introduce any changes in the periodicity of the water flow radically, only in hours or a few days’ time horizon. Both storage and run-of-the river plants can, however, short-cut river stretches (‘bypass sections), which will experience dramatically reduced flow in most of the year.

The habitat conditions are directly affected by the flow and related hydraulic variables such as water depth, water velocity and water-covered areas, and new management practises aim at keeping or restoring natural flow regimes (Poff et al., 2017). Water temperatures are key factors in the development and growth of salmonids (Jonsson and Jonsson, 2011) and are also to a large extent determined by the volumes of water available. The development of the substrate will in longer time horizon be directly affected by the changes in the water flow regime. The functioning of measures presented in this report are also directly dependent on the availability of water and can rarely be implemented without also considering the water flow regime.

=Environmental flow measures=
The various measures to mitigate issues concerning environmental flow are listed below.

<gallery widths=200px heights=200px>
GLOMMA_BYPASS_SQUARE.png|[[Mitigating reduced annual flow and low flow measures]]
stranding_ex_square.png|[[Mitigating rapid, short-term variations in flow (hydro-peaking operations)]]
bjorset_regulated_square.png|[[Mitigating reduced flood peaks, magnitudes, and frequency]]
</gallery>

=Relevant literature=

Jonsson, B. and Jonsson, N. 2011. Ecology of Atlantic Salmon and Brown Trout - Habitat as template for life histories. Springer publishing.

Poff, N.L., Allan, J.D., Bain, M.B., Karr, J.R., Prestegaard, K.L., Richter, B.D., Sparks, R.E. and stromberg, J.C. 1997. The Natural Flow Regime: A paradign fo river conservation and restoration. BioScience 47, 769-784.

[[Category: Types of problems]]

Mitigating reduced flood peaks, magnitudes, and frequency

2020-05-03T13:44:19Z

Dominique Courret:

[[file:icon_operation.png|right|150px|link=[[Environmental flow]]]]
[[file:icon_sediment.png|right|150px|link=[[Sediments]]]]

Note that this measure is included in both the environmental flow and sediment categories. In certain FIThydro deliverables the sediment measure is referred to as "Hydraulic conditions for sediment transport".

=Introduction=
[[file:mitigating_flood_orkla.png|thumb|500px|Figure 1: The disappearance of floods in Orkla in mid-Norway due to the river regulation. The blue graph is the observed flow before regulation, while the orange is the flow after regulation. Note that the data series are shown for different time periods.]]

Reservoir-based hydropower will normally lead to a dramatic reduction in floods, unless the flood occurs when the reservoir is more or less filled, or the reservoir is small compared to the inflow. Some reservoirs are built for this purpose, i.e. flood protection. The ecological function of floods to the river system will then also disappear. The reduced frequency of flooding events may result in a deterioration of habitat quality, both by the silting of spawning habitats and the clogging of sheltered habitats. Floods act as 'habitat fresheners' as they remobilise the river bed material, if the floods are sufficiently large and flush out finer sediment fractions. In later sections of this document, habitat measures to refresh the substrate have been described, which will reinstate the natural substrate conditions and improve the habitat. Reinstating floods is one way of refreshing the substrate with use of the flow.
Floods can also have other ecological functions, for instance to facilitate migration and to attract fish for spawning. These floods (freshets) are typically smaller than the natural, annual flood, but the river regulation can also reduce these floods. Such freshets are usually named attraction flow to initiate upstream migration and trigger flow to initiate downstream migration. These floods can also be reinstated, and similar to floods to remobilise the substrate, the magnitude, timing and frequency of these should be when the ecological function is maximised, and the losses in power production minimised.

=[[Methods, tools, and devices]]=

==During planning==
A hydrologic analysis of flood events before and after regulation will also provide data to support the likelihood that reductions in flood frequencies have reduced, or may in the future reduce, long-term production by causing habitat deterioration. To what extent the habitat has been degraded, can be assessed by habitat mapping [1].

Some studies make a distinction between armoured and paved layers, related to the resistance of surface layers to floods, e.g. less than 10 years for armour, more than 100 years for pavement. The break-up of the armour layer has been observed for floods with a recurrence interval of at least 7 to 10 years. When the break-up of the armour layer occurs, there is a significant increase in the bedload discharge.

==During implementation==
If properly designed gates and valves are in place, the introduction of a new flow regime would simply be to release the defined water flows at the right time of the day and year. If the existing infrastructure cannot release the proposed flow regime, retrofitting of the dam or any other location the water should be released from, must be carried out.

==During operation==
Hydropower operators must normally document that environmental restrictions are followed, and they would have standard monitoring systems (gauging stations) in place. The improvements in the substrate composition and habitat conditions can be measured by for instance measuring the interstitial space.

Shelter for juvenile salmonids can be measured with a simple method where the number and depth of interstitial species within a given area is counted with use of a rubber tube [2]. The number of spaces of varying length are weighed according to their depth and then summed. The number of interstitial spaces within an area of 50 cm * 50 cm, limited by e.g. a steel-frame (Figure 4-5), is counted and the depth registered. The sizes of interstitial spaces are determined based on how far down between the rocks the hose can be inserted.

The effect of the released environmental flow must be surveyed by assessing the development of the fish population, e.g. by monitoring species composition, densities and age structure of populations, number of smolts, etc.

=Relevant MTDs and test cases=
{{Suitable MTDs for Mitigating reduced flood peaks, magnitudes, and frequency}}

=Classification Table=
{{Mitigating reduced flood peaks, magnitudes and frequency}}

=Relevant literature=

[1] Forseth, T. and Harby, A. 2014. Handbook for Environmental design in Regulated salmon Rivers. NINA Special Reports 53. Trondheim: Norwegian Institute for Nature Research.

[2] Finstad, A.G., Einum, S., Ugedal, O. and Forseth, T. 2009. Spatial distribution of limited resources and local density regulation in juvenile Atlantic salmon. Journal of Animal Ecology 78: 226-235.

[[category:Measures]][[Category:Environmental flow measures]][[Category:Sediment measures]]

Mitigating rapid, short-term variations in flow (hydro-peaking operations)

2020-05-03T13:36:06Z

Dominique Courret:

[[file:icon_operation.png|right|150px|link=[[Environmental flow]]]]

=Introduction=
[[file:peaking_params.png|thumb|500px|Figure 1: The figure illustrates the hydropeaking parameters flow ratio (amplitude of change), speed of change and frequency of change in water flow/level. Source [3].]]
[[file:stranding_ex.png|thumb|250px|Figure 2: Fish using the areas identified by red colour will have a risk of stranding when the water level drops rapidly.]]

Hydropeaking refers to hydropower operations that are characterized by more rapid and frequent changes in power production than typical base-load hydropower production. If the water is released into a river, rapid fluctuations in discharge and water level may cause negative impacts to the riverine ecosystem. The severity of the hydropeaking can be categories according to the magnitude of changes in flow, the frequency of the changes, and the timing of the changes, i.e. what time of the day and year the hydropeaking happens.

Bakken et al. [1] defines measures to reduce the impacts from hydropeaking operations into three types; i) operational measures that involves adjusting the magnitude, speed of change, frequency and timing of change to the better for the ecosystem exposed to hydropeaking, ii) physical changes in the river system downstream the outlet of the hydropower plant, and iii) technical measures directly on the power plant/infrastructure, i.e. a technical setup that allows a wider range of turbine discharges, slower stop and start-up, etc.

The measures presented in the following are all related to changes in flow.

=[[Methods, tools, and devices]]=
==During planning==
A group of experienced Norwegian scientists summed of a large research project on environmental impacts from hydropeaking operations (CEDREN EnviPEAK - www.cedren.no) by defining a categorisation system for environmentally-adapted hydropeaking operations. The system was developed based on research from EnviPEAK, other similar studies in Norway and across the world, and the expert judgment of the involved scientists. The system was developed primarily based on knowledge about salmonids’ response to hydropeaking. This system is a set of recommendations, seem to have been adopted as standard requirements for hydropeaking operations in Norway, when the environmental terms of operations are revised, or new licences granted. [[COSH-tool]] can be used to find the relevant hydropeaking parameters.

[[file:peaking_params_table.png|600px|Effect factors, indicators and criteria for characterisation (from [1] and [2].]]

The full categorisation system published in [1] and [2] also includes the dimension of assessing the vulnerability of the ecosystem exposed to hydropeaking. The vulnerability is given by assessing factors such as effective population size, degree of limitations in recruitment, habitat degradation, reduced water temperatures and percentage of impacted river length compared to total length. The combined assessment of the effect factors and the vulnerability will give the total and overall impact assessment.

==During implementation==
If the technical system is properly designed with respect to providing environmentally adapted hydropeaking operations, the introduction of a new flow regime would simply be to release the defined water flows at the right speed and time of the day and year. If the existing infrastructure cannot release support slower ramping rates, adjusted water flow and the flexibility of the frequency and timing, a re-building of the infrastructure might be needed.

==During operation==
A new flow regime better adapted to the ecosystem tolerance of hydropeaking operations would normally not introduce any extra maintenance. Hydropower operators must normally document that the environmental restrictions are followed, and would have standard monitoring systems (gauging stations) in place. It should be ensured that the monitoring is made with sufficiently high resolution to capture the rapid changes in water flow due to hydropeaking.

The positive environmental effect of the released environmental flow must be surveyed by assessing the development of the fish population, e.g. by monitoring species composition, densities and age structure of populations, number of smolts, etc.

=Relevant MTDs and test cases=
{{Suitable MTDs for Mitigating rapid, short-term variations in flow (hydro-peaking operations)}}

=Classification table=
{{Mitigating rapid, short-term variations in flow (hydro-peaking operations)}}

=Relevant literature=

[1] Bakken, T.H., Forseth, T. and Harby, A (Eds) 2016. Miljovirkninger av effecktkjoring: Kunnskapsstatus og rad til forvaltning og industri (in Norwegian).

[2] Harby, A., Forseth, T., Ugedal, O., Bakken, T.H. and Sauterleute, J. 2016. A method to assess impacts from hydropeaking. Proceedings, 11th International Symposium on Ecohydraulics, Melbourne, Australia.

[3] Harby, A. and Noack, M. 2013. Rapid flow fluctuations and impacts on fish and the aquatic ecosystem. In Maddock et al (eds.) 2013. Pp 323-336.

[[category:measures]][[category:Environmental flow measures]]

Mitigating rapid, short-term variations in flow (hydro-peaking operations)

2020-05-03T13:32:29Z

Dominique Courret:

[[file:icon_operation.png|right|150px|link=[[Environmental flow]]]]

=Introduction=
[[file:peaking_params.png|thumb|500px|Figure 1: The figure illustrates the hydropeaking parameters flow ratio (amplitude of change), speed of change and frequency of change in water flow/level.]]
[[file:stranding_ex.png|thumb|250px|Figure 2: Fish using the areas identified by red colour will have a risk of stranding when the water level drops rapidly.]]

Hydropeaking refers to hydropower operations that are characterized by more rapid and frequent changes in power production than typical base-load hydropower production. If the water is released into a river, rapid fluctuations in discharge and water level may cause negative impacts to the riverine ecosystem. The severity of the hydropeaking can be categories according to the magnitude of changes in flow, the frequency of the changes, and the timing of the changes, i.e. what time of the day and year the hydropeaking happens.

Bakken et al. [1] defines measures to reduce the impacts from hydropeaking operations into three types; i) operational measures that involves adjusting the magnitude, speed of change, frequency and timing of change to the better for the ecosystem exposed to hydropeaking, ii) physical changes in the river system downstream the outlet of the hydropower plant, and iii) technical measures directly on the power plant/infrastructure, i.e. a technical setup that allows a wider range of turbine discharges, slower stop and start-up, etc.

The measures presented in the following are all related to changes in flow.

=[[Methods, tools, and devices]]=
==During planning==
A group of experienced Norwegian scientists summed of a large research project on environmental impacts from hydropeaking operations (CEDREN EnviPEAK - www.cedren.no) by defining a categorisation system for environmentally-adapted hydropeaking operations. The system was developed based on research from EnviPEAK, other similar studies in Norway and across the world, and the expert judgment of the involved scientists. The system was developed primarily based on knowledge about salmonids’ response to hydropeaking. This system is a set of recommendations, seem to have been adopted as standard requirements for hydropeaking operations in Norway, when the environmental terms of operations are revised, or new licences granted. [[COSH-tool]] can be used to find the relevant hydropeaking parameters.

[[file:peaking_params_table.png|600px|Effect factors, indicators and criteria for characterisation (from [1] and [2].]]

The full categorisation system published in [1] and [2] also includes the dimension of assessing the vulnerability of the ecosystem exposed to hydropeaking. The vulnerability is given by assessing factors such as effective population size, degree of limitations in recruitment, habitat degradation, reduced water temperatures and percentage of impacted river length compared to total length. The combined assessment of the effect factors and the vulnerability will give the total and overall impact assessment.

==During implementation==
If the technical system is properly designed with respect to providing environmentally adapted hydropeaking operations, the introduction of a new flow regime would simply be to release the defined water flows at the right speed and time of the day and year. If the existing infrastructure cannot release support slower ramping rates, adjusted water flow and the flexibility of the frequency and timing, a re-building of the infrastructure might be needed.

==During operation==
A new flow regime better adapted to the ecosystem tolerance of hydropeaking operations would normally not introduce any extra maintenance. Hydropower operators must normally document that the environmental restrictions are followed, and would have standard monitoring systems (gauging stations) in place. It should be ensured that the monitoring is made with sufficiently high resolution to capture the rapid changes in water flow due to hydropeaking.

The positive environmental effect of the released environmental flow must be surveyed by assessing the development of the fish population, e.g. by monitoring species composition, densities and age structure of populations, number of smolts, etc.

=Relevant MTDs and test cases=
{{Suitable MTDs for Mitigating rapid, short-term variations in flow (hydro-peaking operations)}}

=Classification table=
{{Mitigating rapid, short-term variations in flow (hydro-peaking operations)}}

=Relevant literature=

[1] Bakken, T.H., Forseth, T. and Harby, A (Eds) 2016. Miljovirkninger av effecktkjoring: Kunnskapsstatus og rad til forvaltning og industri (in Norwegian).

[2] Harby, A., Forseth, T., Ugedal, O., Bakken, T.H. and Sauterleute, J. 2016. A method to assess impacts from hydropeaking. Proceedings, 11th International Symposium on Ecohydraulics, Melbourne, Australia.

[[category:measures]][[category:Environmental flow measures]]

Mitigating reduced annual flow and low flow measures

2020-05-03T13:18:55Z

Dominique Courret:

[[file:icon_operation.png|right|150px|link=[[Environmental flow]]]]

=Introduction=
[[file:lundesokna_high_low.png|thumb|500px|Figure 1: The photos show Lundesokna in central Norway at different water flows.]]
[[file:Building_block_method.png|thumb|500px|Figure 2: An example of the building block method showing average flow curves before and after regulation, and the key flow blocks. Duration (x-axis, width) multiplied by flow (y-axis, height) provides a measure of the volume of water in question (area of the blocks) and these can be summed to give the reach's "water pool". 1=egg survival and winter habitat, 2=smolt out-migration, 3=flushing flows, 4=juvenile fish growth, 5=juvenile fish habitat, 6=artificial freshets to facilitate angling interests and promote spawning migration, 7=spawning. The colours indicate prioritisation – from orange (high) to blue (low), based on the severity of identified hydrologic bottlenecks. Source [4].]]
[[file:gauge2.png|250px|thumb|Figure 3: Gauging station monitoring water level and water flow]]
[[file:gauge1.jpg|250px|thumb|Figure 4: Gauging station monitoring water level and water flow]]

Bypass sections of a river regulation will typically experience dramatic reductions in total, annual flow, as large volumes of water are withdrawn for the purpose of producing electricity. The changes will depend on the hydrology characteristics, regulation capacity, the turbine characteristics (i.e. minimum and maximum capacities), the power production pattern and the minimum flow requirements. In cases with limited regulation capacities, spill of water will happen when the inflow is higher than the intake ponds can store and the turbines can utilise. How often this will happen is determined by the hydrological characteristics of the river.

The challenge related to reductions in total, annual flow would be to define ‘how much water is needed to sustain essential habitat qualities’, given dramatic reduced most of the time. This is the most common scientific task related to environmental flow assessments in bypass sections, and downstream the outlet of the hydropower plants in periods the hydropower plant is not in operation. A large set of approaches are available, spanning from simple statistical methods to comprehensive, holistic modelling approaches, with the aim of defining how much water should be released at what period of the year. The more simplified methods would require only a water flow timeseries, while the more advanced would needed detailed measurements of the topography and information about ecological preferences of various flow regimes.

=[[Methods, tools, and devices]]=
==During planning==
The most common method to define environmental flow, or more correctly minimum flow, in Europe is to use of simple statistical criteria [1]. Q95 or variants of this is used in several countries as benchmark for the lowest flow releases in rivers with dramatically reduced flows. Q95 refers to the flow that during the natural conditions is exceeded in 95% of the time. Q95 is licence agreement defined as a constant flow that should be released throughout the year, or as a flow level defined based on natural flows during summer and winter, respectively, giving different statistic of flow regime during summer and winter. Bakken et al. [2] concluded in their review where the practice in a number of European countries were assessed, that the environmental flow requirements are typically in the range 5-10 % of mean annual flow.
In some countries and in selected cases more advanced approaches are used, taking into account the natural variation in flow regime, and the varying flow requirements over the year. The building Block Method (BBM) [3] is one approach, while the environmental design concept [4] has received very much positivism in Norway from both the hydropower industry, management authorities as well as various stakeholder groups. The Building Block Method intends to define flow regimes that are closer to the natural variation in water flow, i.e. mimicking natural floods, freshets and low flow periods. The environmental design concept aims at identifying the factors limiting the development of the fish population, which can be directly related to the flow regime, and then define the most efficient measures to the lowest cost. The environmental design concept also introduces the ‘water bank’ idea, where the water available for environmental purposes is released during the periods it is most needed.
Hydraulic habitat modelling is a highly sophisticated approach that has been developed since the 1980’s, where the PHABSIM was one of the first computer program for such analysis. Hydraulic habitat modelling has been used in several cases where more detailed studies are required before the water flow regime can be defined, in addition to a large range of purely scientific studies. Hydraulic habitat modelling aims at identifying flows where the habitat conditions are suitable, based on various groups of species’ preferences for hydraulic variable such as water velocity, water depth and substrate conditions. This would sometimes reveal that increasing water flow will not always increase the areas of suitable habitat. Such studies have been carried out mostly related to defining suitable conditions for fish, but is in some cases also applied for benthic invertebrates. Hydraulic habitat modelling would require a 2- or 3-dimensional hydraulic model taking flow as input, and a set of ranges where water velocities, depths and substrate conditions are suitable. Casimir is such a tool that is developed in Germany, but applied in several rivers across Europe, as well as outside Europe. Hydraulic habitat modelling must be considered an ecosystem-based analysis, in contrast to the much simpler statistical approaches, such as applying Q95.

==During implementation==
If properly designed gates and vales are in place, the introduction of a new flow regime would simply be to release the defined water flows at the right time of the day and year. If the existing infrastructure cannot release the proposed flow regime, re-building of the dam or any other location the water should be released from, must be carried out.

==During operation==
Hydropower operators must normally document that the environmental restrictions are followed, and would have standard monitoring systems (gauging stations) in place. The effect of the released environmental flow must be surveyed by assessing the development of the fish population, e.g. by monitoring species composition, densities and age structure of populations, number of smolts, etc.

=Relevant MTDs and test cases=
{{Suitable MTDs for Mitigating reduced annual flow and low flow measures}}

=Classification table=
{{Mitigating reduced annual flow and low flow measures}}

=Relevant literature=

[1] Bakken et al., WFD-report.

[2] Bakken, T.H., Zinke, P., Melcher, A., Sundt, H., Vehanen, T., Jorde, K. and Acreman, M. 2012. Setting Environmental flows in regulated rivers. SINTEF report Serial No. TR A7246. ISBN 978-82-594-3529-3.

[3] Tharme, R., King, J. and De Villiers, M.S. 1998. Environmental Flow Assessments for Rivers: Manual for the Building Block Methodology. Updated adition. WRC Report No TT 354/08.

[4] Forseth, T. and Harby, A. 2014. Handbook for Environmental design in Regulated salmon Rivers. NINA Special Reports 53. Trondheim: Norwegian Institute for Nature Research.

[[Category:Measures]][[category:Environmental flow measures]]

Environmental flow

2020-05-03T13:16:37Z

Dominique Courret:

=Introduction=
[[File:e-flow.png|thumb|500px|Figure 1: Environmental flow release in Mandal River, Norway]]

Hydropower projects will in most cases change the flow pattern of the affected rivers. The changes in flow are very site-specific and dependent on how the actual project is designed. A hydropower project with a large reservoir for storage of water (‘reservoir-based hydropower’) generally allows much larger changes in flow than a run-of-the river plant. Reservoir-based hydropower can store water from the wet to the dry season and can hence introduce large changes in the periodicity of the flow. Reservoir-based hydropower can also store all or parts of floods, and will typically reduce both the magnitude, peaks and frequency of floods. Run-of-the river plants have limited storage capabilities and will not introduce any changes in the periodicity of the water flow radically, only in hours or a few days’ time horizon. Both storage and run-of-the river plants can, however, short-cut river stretches (‘bypass sections), which will experience dramatically reduced flow in most of the year.

The habitat conditions are directly affected by the flow and related hydraulic variables such as water depth, water velocity and water-covered areas, and new management practises aim at keeping or restoring natural flow regimes [1]. Water temperatures are key factors in the development and growth of salmonids [2] and are also to a large extent determined by the volumes of water available. The development of the substrate will in longer time horizon be directly affected by the changes in the water flow regime. The functioning of measures presented in this report are also directly dependent on the availability of water and can rarely be implemented without also considering the water flow regime.

=Environmental flow measures=
The various measures to mitigate issues concerning environmental flow are listed below.

<gallery widths=200px heights=200px>
GLOMMA_BYPASS_SQUARE.png|[[Mitigating reduced annual flow and low flow measures]]
stranding_ex_square.png|[[Mitigating rapid, short-term variations in flow (hydro-peaking operations)]]
bjorset_regulated_square.png|[[Mitigating reduced flood peaks, magnitudes, and frequency]]
</gallery>

=Relevant literature=

[1] Poff, N.L., Allan, J.D., Bain, M.B., Karr, J.R., Prestegaard, K.L., Richter, B.D., Sparks, R.E. and stromberg, J.C. 1997. The Natural Flow Regime: A paradign fo river conservation and restoration. BioScience 47, 769-784.

[2] Jonsson, B. and Jonsson, N. 2011. Ecology of Atlantic Salmon and Brown Trout - Habitat as template for life histories. Springer publishing.

[[Category: Types of problems]]

Mitigating reduced annual flow and low flow measures

2020-05-03T13:07:00Z

Dominique Courret:

[[file:icon_operation.png|right|150px|link=[[Environmental flow]]]]

=Introduction=
[[file:lundesokna_high_low.png|thumb|500px|Figure 1: The photos show Lundesokna in central Norway at different water flows.]]
[[file:Building_block_method.png|thumb|500px|Figure 2: An example of the building block method showing average flow curves before and after regulation, and the key flow blocks. Duration (x-axis, width) multiplied by flow (y-axis, height) provides a measure of the volume of water in question (area of the blocks) and these can be summed to give the reach's "water pool". 1=egg survival and winter habitat, 2=smolt out-migration, 3=flushing flows, 4=juvenile fish growth, 5=juvenile fish habitat, 6=artificial freshets to facilitate angling interests and promote spawning migration, 7=spawning. The colours indicate prioritisation – from orange (high) to blue (low), based on the severity of identified hydrologic bottlenecks.]]
[[file:gauge2.png|250px|thumb|Figure 3: Gauging station monitoring water level and water flow]]
[[file:gauge1.jpg|250px|thumb|Figure 4: Gauging station monitoring water level and water flow]]

Bypass sections of a river regulation will typically experience dramatic reductions in total, annual flow, as large volumes of water are withdrawn for the purpose of producing electricity. The changes will depend on the hydrology characteristics, regulation capacity, the turbine characteristics (i.e. minimum and maximum capacities), the power production pattern and the minimum flow requirements. In cases with limited regulation capacities, spill of water will happen when the inflow is higher than the intake ponds can store and the turbines can utilise. How often this will happen is determined by the hydrological characteristics of the river.

The challenge related to reductions in total, annual flow would be to define ‘how much water is needed to sustain essential habitat qualities’, given dramatic reduced most of the time. This is the most common scientific task related to environmental flow assessments in bypass sections, and downstream the outlet of the hydropower plants in periods the hydropower plant is not in operation. A large set of approaches are available, spanning from simple statistical methods to comprehensive, holistic modelling approaches, with the aim of defining how much water should be released at what period of the year. The more simplified methods would require only a water flow timeseries, while the more advanced would needed detailed measurements of the topography and information about ecological preferences of various flow regimes.

=[[Methods, tools, and devices]]=
==During planning==
The most common method to define environmental flow, or more correctly minimum flow, in Europe is to use of simple statistical criteria (Bakken et al., WFD-report). Q95 or variants of this is used in several countries as benchmark for the lowest flow releases in rivers with dramatically reduced flows. Q95 refers to the flow that during the natural conditions is exceeded in 95% of the time. Q95 is licence agreement defined as a constant flow that should be released throughout the year, or as a flow level defined based on natural flows during summer and winter, respectively, giving different statistic of flow regime during summer and winter. Bakken et al. (2012) concluded in their review where the practice in a number of European countries were assessed, that the environmental flow requirements are typically in the range 5-10 % of mean annual flow.
In some countries and in selected cases more advanced approaches are used, taking into account the natural variation in flow regime, and the varying flow requirements over the year. The building Block Method (BBM) (Tharme and King, 1998) is one approach, while the environmental design concept (Forseth and Harby, 2014) has received very much positivism in Norway from both the hydropower industry, management authorities as well as various stakeholder groups. The Building Block Method intends to define flow regimes that are closer to the natural variation in water flow, i.e. mimicking natural floods, freshets and low flow periods. The environmental design concept aims at identifying the factors limiting the development of the fish population, which can be directly related to the flow regime, and then define the most efficient measures to the lowest cost. The environmental design concept also introduces the ‘water bank’ idea, where the water available for environmental purposes is released during the periods it is most needed.
Hydraulic habitat modelling is a highly sophisticated approach that has been developed since the 1980’s, where the PHABSIM was one of the first computer program for such analysis. Hydraulic habitat modelling has been used in several cases where more detailed studies are required before the water flow regime can be defined, in addition to a large range of purely scientific studies. Hydraulic habitat modelling aims at identifying flows where the habitat conditions are suitable, based on various groups of species’ preferences for hydraulic variable such as water velocity, water depth and substrate conditions. This would sometimes reveal that increasing water flow will not always increase the areas of suitable habitat. Such studies have been carried out mostly related to defining suitable conditions for fish, but is in some cases also applied for benthic invertebrates. Hydraulic habitat modelling would require a 2- or 3-dimensional hydraulic model taking flow as input, and a set of ranges where water velocities, depths and substrate conditions are suitable. Casimir is such a tool that is developed in Germany, but applied in several rivers across Europe, as well as outside Europe. Hydraulic habitat modelling must be considered an ecosystem-based analysis, in contrast to the much simpler statistical approaches, such as applying Q95.

==During implementation==
If properly designed gates and vales are in place, the introduction of a new flow regime would simply be to release the defined water flows at the right time of the day and year. If the existing infrastructure cannot release the proposed flow regime, re-building of the dam or any other location the water should be released from, must be carried out.

==During operation==
Hydropower operators must normally document that the environmental restrictions are followed, and would have standard monitoring systems (gauging stations) in place. The effect of the released environmental flow must be surveyed by assessing the development of the fish population, e.g. by monitoring species composition, densities and age structure of populations, number of smolts, etc.

=Relevant MTDs and test cases=
{{Suitable MTDs for Mitigating reduced annual flow and low flow measures}}

=Classification table=
{{Mitigating reduced annual flow and low flow measures}}

=Relevant literature=

Bakken et al., WFD-report.

Bakken, T.H., Zinke, P., Melcher, A., Sundt, H., Vehanen, T., Jorde, K. and Acreman, M. 2012. Setting Environmental flows in regulated rivers. SINTEF report Serial No. TR A7246. ISBN 978-82-594-3529-3.

Tharme, R., King, J. and De Villiers, M.S. 1998. Environmental Flow Assessments for Rivers: Manual for the Building Block Methodology. Updated adition. WRC Report No TT 354/08.

Forseth, T. and Harby, A. 2014. Handbook for Environmental design in Regulated salmon Rivers. NINA Special Reports 53. Trondheim: Norwegian Institute for Nature Research.

[[Category:Measures]][[category:Environmental flow measures]]

Environmental flow

2020-05-03T12:51:12Z

Dominique Courret:

=Introduction=
[[File:e-flow.png|thumb|500px|Figure 1: Environmental flow release in Mandal River, Norway]]

Hydropower projects will in most cases change the flow pattern of the affected rivers. The changes in flow are very site-specific and dependent on how the actual project is designed. A hydropower project with a large reservoir for storage of water (‘reservoir-based hydropower’) generally allows much larger changes in flow than a run-of-the river plant. Reservoir-based hydropower can store water from the wet to the dry season and can hence introduce large changes in the periodicity of the flow. Reservoir-based hydropower can also store all or parts of floods, and will typically reduce both the magnitude, peaks and frequency of floods. Run-of-the river plants have limited storage capabilities and will not introduce any changes in the periodicity of the water flow radically, only in hours or a few days’ time horizon. Both storage and run-of-the river plants can, however, short-cut river stretches (‘bypass sections), which will experience dramatically reduced flow in most of the year.

The habitat conditions are directly affected by the flow and related hydraulic variables such as water depth, water velocity and water-covered areas, and new management practises aim at keeping or restoring natural flow regimes (Poff et al. 1997). Water temperatures are key factors in the development and growth of salmonids (Jonsson and Jonsson 2011) and are also to a large extent determined by the volumes of water available. The development of the substrate will in longer time horizon be directly affected by the changes in the water flow regime. The functioning of measures presented in this report are also directly dependent on the availability of water and can rarely be implemented without also considering the water flow regime.

=Environmental flow measures=
The various measures to mitigate issues concerning environmental flow are listed below.

<gallery widths=200px heights=200px>
GLOMMA_BYPASS_SQUARE.png|[[Mitigating reduced annual flow and low flow measures]]
stranding_ex_square.png|[[Mitigating rapid, short-term variations in flow (hydro-peaking operations)]]
bjorset_regulated_square.png|[[Mitigating reduced flood peaks, magnitudes, and frequency]]
</gallery>

=Relevant literature=

Poff, N.L., Allan, J.D., Bain, M.B., Karr, J.R., Prestegaard, K.L., Richter, B.D., Sparks, R.E. and stromberg, J.C. 1997. The Natural Flow Regime: A paradign fo river conservation and restoration. BioScience 47, 769-784.

Jonsson, B. and Jonsson, N. 2011. Ecology of Atlantic Salmon and Brown Trout - Habitat as template for life histories. Springer publishing.

[[Category: Types of problems]]

Environmental flow

2020-05-03T12:44:55Z

Dominique Courret:

=Introduction=
[[File:e-flow.png|thumb|500px|Figure 1: Environmental flow release in Mandal River, Norway]]

Hydropower projects will in most cases change the flow pattern of the affected rivers. The changes in flow are very site-specific and dependent on how the actual project is designed. A hydropower project with a large reservoir for storage of water (‘reservoir-based hydropower’) generally allows much larger changes in flow than a run-of-the river plant. Reservoir-based hydropower can store water from the wet to the dry season and can hence introduce large changes in the periodicity of the flow. Reservoir-based hydropower can also store all or parts of floods, and will typically reduce both the magnitude, peaks and frequency of floods. Run-of-the river plants have limited storage capabilities and will not introduce any changes in the periodicity of the water flow radically, only in hours or a few days’ time horizon. Both storage and run-of-the river plants can, however, short-cut river stretches (‘bypass sections), which will experience dramatically reduced flow in most of the year.

The habitat conditions are directly affected by the flow and related hydraulic variables such as water depth, water velocity and water-covered areas, and new management practises aim at keeping or restoring natural flow regimes (Poff et al. 1997). Water temperatures are key factors in the development and growth of salmonids (Jonsson and Jonsson 2011) and are also to a large extent determined by the volumes of water available. The development of the substrate will in longer time horizon be directly affected by the changes in the water flow regime. The functioning of measures presented in this report are also directly dependent on the availability of water and can rarely be implemented without also considering the water flow regime.

=Environmental flow measures=
The various measures to mitigate issues concerning environmental flow are listed below.

<gallery widths=200px heights=200px>
GLOMMA_BYPASS_SQUARE.png|[[Mitigating reduced annual flow and low flow measures]]
stranding_ex_square.png|[[Mitigating rapid, short-term variations in flow (hydro-peaking operations)]]
bjorset_regulated_square.png|[[Mitigating reduced flood peaks, magnitudes, and frequency]]
</gallery>

[[Category: Types of problems]]